PNNL

Abstract

Accurately modeled Biogenic Volatile Organic Compound (BVOC) emissions are an essential input to atmospheric chemistry simulations of ozone and particle formation. BVOC emission models originate from leaf and branch level measurements with scaling to regional or larger spatial levels based on vegetation landcover data derived Basal Emission Factors (BEFs), but they generally lack validation by regional scale measurements. We directly assess isoprene emission-factor databases for BVOC emission models by deriving BEFs from direct airborne fluxes aggregated at 2 km resolution and averaged spatially over ecoregions covering ~10,000 km of California. Ecoregion averaged BEFs from the landcover used by the Model of Emissions of Gases and Aerosols from Nature (MEGAN) v. 2.1 BVOC emission model agreed within 10% (r2=0.82) with measured BEFs, with few discrepancies (either overestimation or underestimation). Independently, we found the BVOC emission model from the California Air Resources Board averaged for the same flight times and averaged for the same flux footprints as actual measured area emissions agreed on average within 20% (r2=0.96). We show that the choice of model landcover input data has the most critical influence on model-measurement agreement and the uncertainty in meteorology inputs has a lesser impact at scales relevant to regional air quality modeling.